1. Field of the Invention
This invention relates to tubular formed products, more particularly, the process of shaping or forming tubular shapes, and specifically to the process of forming a tubular member including an integral bracket.
2. Description of the Related Art
The history and background of making tubes and pipes will not be addressed in any significant detail herein; however common methods for forming tubular products include roll forming, extrusion, hydroforming, casting, and machining. Each method has its own individual drawbacks discussed below.
Roll forming is a process which imparts a tubular shape to flat stock by imparting a radius to the sheet stock as it is passed linearly, through a plurality of rollers. The rollers, referred to as roller dies, are precision made for each job. As the sheet metal passes through each set of rollers, the rollers change the profile of the metal. Through successive rolling operations the roller stations may create profiles which are substantially closed, but none which are tightly controlled. These rolled profiles have varied applications in manufacturing, commercial building, aerospace and other sectors however are inapplicable to forming tightly sealed tubing since rolling can not fully and tightly close a tubular seam with an attached bracket.
Another method for creating tubular structures is by a process called extrusion. Extruded tubular articles are formed by forcing material through a die containing the material's desired final cross section. The material being extruded is typically forced through the die by a large hydraulic press, causing the material to locally ‘flow’ through the die resulting in the final shape. Product formed by this method may contain well formed seams; however this process is only suited to products containing a uniform cross section, such as rails or pipe, as extrusion machines are unable to produce tubular members which have attached non-uniform sections such as brackets or flanges.
Hydro-forming is process which uses a pressurized fluid to shape and form a part. Hydro-forming is principally described as either sheet hydro-forming, or tube hydro-forming, depending on the form of the blank inserted into the machine.
In sheet based hydro-forming, a blank is placed against a male portion of the die, and a high pressure fluid is applied to the opposite side of the sheet forcing the material to conform to the male half of the die. Localized thinning and wrinkling of the sheet are common occurrences, and closed tubular forms can not be formed by this method alone.
Tube based hydro-forming places a tubular shaped blank into a hydroforming tool and then applies pressurized fluid to the interior walls of the tube causing the tube to expand to the limits of the die chamber. The process is commenced by sealing the tubular blank, and injecting hydraulic fluid into the sealed tube through one of two axial end punches. These axial end punches are movable and are also used to apply an axial load upon the blank to feed material towards the center of the expanding tube. The tubular blank must contain a wall thickness which is far thicker than required of the final form in order to accommodate the localized thinning that occurs when the tube expands toward the limits of the die chamber. Further, the blank form itself must be substantially fluid-tight in order to contain the hydroforming fluid. This fluid-tight requirement precludes the use of open form brackets attached to tubular members.
Another method of making complex tubular products is by casting. In casting, molten metal is supplied into a mold form where it then cools, solidifying into its final product shape. This method often traps air and other impurities in the casting substantially weakening the part. Further, the properties of the material made by casting are not metallurgically nor structurally similar, and are often not as strong as a cold worked stamped products of the same shape. Castings often requiring a separate annealing and heat treatment process to approach similar product strength. Further still, casting requires specialized alterations to the final part such as parting lines, and ejector pins, each of which affects the geometry of the part.
Yet another method for making tubular work pieces is via machining. The advent of computer aided machining now allows for complex shapes to be milled from solid billet material. However, when it comes to machining tubular products, the results are limited to those shapes which may be plunge cut, broached, or turned on a lathe. Similar to castings, the properties of the billet material differ metallurgically and structurally from stamped material due to the lack of cold working of the material.
Tubular products with attached brackets may be achieved using welding. A tubular form may be manufactured separately from the bracket. The parts are then brought into contact, and a welding tool locally heats the parts causing localized sections of the parts to melt and flow together. When the parts cool, they will become conjoined. This localized melting and reforming alters the properties of the base metals, creating stress risers and other aberrancies which affect the structural integrity of the components due to their altered crystalline form.
U.S. Pat. Nos. 6,920,772; 6,904,677; 6,892,559; 6,591,648; and 4,991,419 further describe the formation of tubular products by roll forming, hydro-forming, and other techniques, and are incorporated herein by reference.
As noted above, roll formed products are unable to produce tightly formed seams. Extruded tubes are inherently linear, and are unable to process brackets integral to the tubing. Sheet hydro-forming, similar to roll form materials, is unable to form tightly closed forms. Tube hydro-forming is not an available option, as brackets attached to the tubular form interfere with the sealed surfaces necessary to form the tube. Casting, machining, and welding all result in a non-identical metallurgical structure and strength. Consequently, none of the methods described above are appropriate for manufacturing of a tubular work pieces with a precision seam attached to an integral bracket.
The invention described herein solves the disadvantages noted in the prior art above by providing a method for forming flat metal stock into a tubular form with a tightly formed precision seam attached to integral flange or bracket. Further, the inventive process described forms flat metal stock into a tubular form with a tightly formed precision seam attached to integral flange or bracket further containing one or more notches coined into the tube.